The present invention relates to an image recording and reproduction apparatus, and more specifically, to a contour compensation circuit (image enhancer) used for a signal processing circuit in a VTR, a video display apparatus, a video camera and the like.
The following is a description of the prior art, with reference to FIG. 1 of the appended drawings. An image signal S.sub.a is inputted to an input terminal 31 and is also inputted to a delay line 33 after passing an input matching resistor 32. The delay line 33 delays the signal by a required time t.sub.d. The signal that has been delayed by the delay line 33 is inputted to the positive input of a subtractor 34 and to one of the input terminals of an adder 35. The output side of the delay line 33 is received by a high impedance and so a reflection action is generated at the output terminal of the delay line 33 and this reflected signal is further delayed and transmitted to the input side of the delay line 33. The input signal and the signal that has been delayed by twice the required time 2t.sub.d are added by the input matching resistor 32 and are inputted to the negative input of the subtractor 34. Moreover, the output of the subtractor 34 is supplied to the other input of the adder 35. And a signal of those input image signals and for which the contour portion is emphasized is outputted from the adder 35 to an output terminal 36. Moreover, FIG. 2 shows the signals at various portions, with FIG. 2 (a) showing the image signal S.sub.a that is inputted to the input terminal 31, FIG. 2 (b) showing the signal S.sub.b that is delayed by a time t.sub.d by the delay line 33, FIG. 2 (c) showing the signal S.sub.c which is obtained by addition at the matching resistor 32 of the input signal S.sub.a and the signal reflected at the output terminal of the delay line 33 and delayed by a time 2t.sub.d. FIG. 2 (d) shows the output signals S.sub.d of the subtractor 34, and FIG. 2 (e) shows the output signals S.sub.e of the adder 35 that adds the signals S.sub.b and the signals S.sub.d.
The problem with this prior art is that the noise in the high-frequency band is also emphasized along with the contour portion of the image signal. As a result, this noise becomes conspicuous when the image signal is of low level. Because of this, the degree of emphasis of the contour portion of the image signal can be controlled in accordance with the level of the image signal, but with the prior art, it is difficult to perform such control so that it seems natural.